Thousands of vehicles are repeatedly blowing through E-ZPass lanes in states such as Maryland without an E-ZPass transponder, and the state is doing little to collect the millions of dollars in unpaid tolls.

One car-rental company owes the state nearly $209,000 in unpaid tolls and penalties, despite having received nearly 7,000 letters over four years, according to state figures. Eight other rental companies owe between $80,000 and $200,000 each, with some violations dating back eight years. Individual vehicle owners aren’t paying up, either. About 15,000 owe more than $500 each.

Some losses are inevitable, officials say, but states are now beginning to take steps to collect the unpaid tolls. Three states — Maine, Massachusetts and New Hampshire — recently entered the first-ever reciprocity agreement to pursue vehicle registrations of out-of-state toll violators. In Virginia, vehicle owners with three or more unpaid violations are summoned to a court hearing, where a judge may impose a civil penalty of up to $500 for multiple violations. If an owner ignores the court-ordered fines, the state puts a hold on the vehicle’s registration renewal.

New Jersey has arrested some of its most flagrant toll cheats on theft-of-services charges and recently posted a “Wall of Shame” on the Internet listing toll scofflaws by name and hometown. “The registration holds work,” said Vic Buono, Delaware’s chief of toll operations. “People freak out when they get that.”

More than a few cheaters may have caught on to the fact that the letters sent by Maryland are paper tigers.

Pay, the Maryland Transportation Authority says, or the vehicle’s registration could be suspended. But the Maryland Motor Vehicle Administration hasn’t suspended a vehicle registration for nonpayment of tolls in more than two years. That’s because the authority hasn’t been hitting violators with a $50 citation, which it has to do by law if it wants the MVA to suspend registrations.

Instead, the authority, which operates the state’s eight toll facilities, mails vehicle owners a “notice of toll due.” After 30 days of nonpayment, the authority tacks on a $25 fee. Repeat violators are referred to the state’s central collection unit, which continues to send periodic letters requesting payment. But unlike its practice with other types of debt owed to the state, the unit never reports chronic toll violators to credit-rating agencies.

Del. Stephen Lafferty, D-Baltimore County, said he was “incredulous and livid” when he heard about the issue during a brief legislative hearing this spring. That law-abiding motorists have been paying higher tolls since November only added to his outrage, he said. “Someone owes $200,000, and you’re not going after these people?” Lafferty said. “Those people are taking advantage of the state.”

In total, nearly 650,000 vehicle owners owe about $6.7 million in unpaid tolls dating back five years, according to the authority.

Harold Bartlett, the authority’s executive secretary, said losses so far from unpaid tolls are “very manageable” as a portion of overall revenue and have not affected the authority’s ability to maintain or build toll facilities.

“Obviously, every single dollar is important to us, so we don’t take any comfort in saying it’s a small number,” Bartlett said. “We’re continuing to pursue avenues to get those numbers down.”

Authority officials said they are negotiating with the car-rental companies that owe the most. The agency, citing privacy protections in Maryland’s electronic tolling law, denied a public-records request from The Washington Post for the database that includes the names of the rental companies and other vehicle owners who owe money.

Losses from unpaid tolls amount to a minuscule share of the authority’s revenue, but the debt has grown quickly in recent years. In fiscal 2008, those annual losses amounted to $555,000, or two-tenths of 1 percent of that year’s toll revenue, according to the agency’s figures. Three years later, violators racked up $1.18 million in tolls owed, almost four-tenths of 1 percent of annual toll income.

The losses have mounted as Maryland and governments across the country are increasingly turning to toll revenue to finance transportation construction. The traditional source of such funding — the gas tax — hasn’t kept pace with infrastructure needs, state officials say, and efforts to raise it have failed amid anti-tax sentiments and gasoline price spikes.

Anticipated toll revenue was a critical source of funding for several of the Washington, D.C., area’s newest transportation projects, including the recently opened $2.56 billion Intercounty Connector (ICC) in the Maryland suburbs and the $5.6 billion Metrorail Silver Line extension under construction in Northern Virginia.

“There are so few transportation dollars for maintenance and construction of new roads that you can’t afford to give people a free ride,” said PJ Wilkins, executive director of the E-ZPass Group, which coordinates E-ZPass operations among 14 states.

Meanwhile, technology is making it easier to cheat. The advent of E-ZPass systems in the 1990s eliminated the need for motorists with transponders — or without them — to stop at manned tollbooths or gates. The issue sparked attention locally in 2005 when the Virginia Department of Transportation acknowledged that, for a decade, it had no cameras to catch scofflaws passing through electronic toll lanes on the Dulles Toll Road. Cameras were installed a year later.

Complicating collection efforts in Maryland is the fact that the state recently began using “video tolling.” Vehicles may use E-ZPass lanes without a transponder, and the owner is mailed a photograph of the vehicle along with a “notice of toll due” for a higher toll rate.

Like other states, Maryland is exploring ways to speed traffic by eliminating tollbooths and relying solely on E-ZPass transponders or video tolls, similar to the system on the ICC.

Motorists aren’t ignoring Maryland’s tolls as frequently as in neighboring states, according to figures obtained by The Post. In Virginia, violators account for 1.7 percent of annual toll transactions. In Delaware, the rate is 3.4 percent, and in New Jersey, it’s 1.4 percent.

But the issue hits a particularly sour note in Maryland, where toll rates, which began rising in November, are set to increase again next year, more than doubling at some facilities by July. The board of the once cash-flush authority said it needs more money to pay off construction debt on the ICC and $1 billion worth of express toll lanes on I-95 near Baltimore.

Bartlett said the authority has never followed the 1994 tolling law because it wanted a “more customer-friendly approach” than the law’s automatic $50 citation for going through a tollbooth without an E-Z Pass and referral to District Court for those who refuse to pay the $50. But in May 2010, the MVA determined that by not imposing the $50 citation, the authority was forgoing the option to have a registration suspended.

The tolling authority has turned to the state’s collection unit for vehicle owners who rack up at least $30 in unpaid tolls and fees. Authority officials say they focus on the worst cases because doing so is labor-intensive. The authority referred nearly 700 vehicle owners to the collection unit in fiscal 2012.

Tony Fugett, the unit’s director, said toll violators receive two letters and an occasional automated phone call requesting payment. After that, they receive a letter once a year. The state can deduct money owed from lottery winnings, contractor payments or state income tax refunds, Fugett said. If none of those is applicable, he said, “I guess there’s nothing we’d have in our arsenal other than continuing to contact people.”

Fugett said the unit doesn’t report chronic toll violators to credit-rating agencies, as it does with other types of debtors. He said he had thought the state was suspending those motorists’ vehicle registrations or flagging them for non-renewal until the debt was collected.

After being told that such sanctions hadn’t been imposed in more than two years, Fugett said, “The teeth I thought were there aren’t there anymore.”

The authority proposed legislation this year to allow the MVA to resume suspending vehicle registrations or blocking their renewal. The bill also would have allowed the authority to pursue out-of-state violators more aggressively. They account for a quarter of Maryland’s unpaid tolls, but Maryland does not have reciprocal agreements with other states. Without such pacts, states are unwilling to suspended or revoke registrations to carry out other states’ toll collections.

The bill was introduced late in the legislative session and died in committee.